Zoom optical system

ABSTRACT

A zoom optical system includes in order from a reduction side to a magnification side: a first lens unit having a positive optical power; a second lens unit having a negative optical power; a third lens unit having a positive optical power; and a fourth lens unit having a positive optical power, wherein respective intervals between the above described first, second, third and fourth lens units vary during zooming; a magnification-side conjugate position with respect to a reduction-side conjugate position and a position of a pupil of the above described zoom optical system with respect to a reduction-side conjugate position are substantially immobile respectively across the entire zooming range, and the above described fourth lens unit moves toward the magnification side and an interval between the above described first lens unit and the above described fourth lens unit increases during zooming from a wide-angle end to a telephoto end.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a zoom optical system used for anoptical apparatus such as an image projecting apparatus, an exposureapparatus and the like.

2. Related Background Art

Some optical apparatuses as described above need a zoom optical systemthat is excellent in the telecentricity on the object side and excellentin invariance of positions of the object surface, the image plane andthe exit pupil to a variation of the focal length.

For example, Japanese Patent Application Laid-Open No. 2002-207167 hasdisclosed a zoom optical system suitable for illumination optical systeminstalled in a projection exposure apparatus, that moves a lens unithaving negative refractive power or a lens unit including a lens elementhaving a strong negative refractive power toward an object side as focallength gets shorter so as to make positions of an object surface, animage plane, an entrance pupil and an exit pupil immobile againstvariation of focal length.

In addition, in Japanese Patent Application Laid-Open No. 2002-055279, azoom optical system suitable for a transmission optical system inillumination optical system installed in a projection exposure apparatushas been disclosed. The zoom optical system includes at least four lensunits and at least three lens units moves so as to change the refractivepower arrangement from negative-positive-positive orpositive-positive-negative in the order from the object side to apositive-negative-positive in the order from the object side duringzooming from the wide angle end to the telephoto end and therebypositions of an object surface, an image plane, an entrance pupil and anexit pupil are made immobile against variation of focal length.

Here, it is considered to use a zoom optical system disclosed inJapanese Patent Application Laid-Open No. 2002-207167 and JapanesePatent Application Laid-Open No. 2002-055279 in projection opticalsystem or a part thereof of an image projecting apparatus ofmagnifying/projecting an image of an original formed on a liquid crystalpanel.

However, if liquid crystal panel is disposed on a reduction side focalplane of a zoom optical system disclosed in Japanese Patent ApplicationLaid-Open No. 2002-207167, it is impossible to secure a sufficient backfocus and space for arranging a color synthesizing member at thereduction side. For a so-called 3-plate type image projecting apparatus,a color synthesizing member for synthesizing three color lights of red,green and blue is arranged on the reduction side of a zoom opticalsystem. However, if there is no sufficient back focus as describedabove, it will become impossible to secure a space for arranging thecolor synthesizing member.

In addition, in the zoom optical system disclosed in Japanese PatentApplication Laid-Open No. 2002-207167, a lens unit at the most reductionside has a negative refractive power, and as focal length gets shorter,a lens unit having a positive refractive power arranged on themagnification side of the negative lens unit (a second lens unit) movedtoward the magnification side so that an interval between the both lensunits increases. Therefore, the effective diameter of the positive lensunit will get large. Moreover, since the lens unit at the most reductionside has a negative refractive power, a numerical aperture (NA) on thereduction side will get small.

Here, in Japanese Patent Application Laid-Open No. 2002-207167, such acase where a lens unit at the most reduction side is caused to have apositive refractive power is disclosed. However, since this lens unitsignificantly moves toward the magnification side as the focal lengthgets shorter, the effective diameter of the lens unit will get large ifthe NA on the reduction side is made large.

That is, in this zoom optical system, in a state of the minimum focallength (wide), a plurality of lens units get closer toward an aperturestop side, and as the focal length gets longer, move toward thereduction side focal plane side, and therefore the effective diameter ofthe lens unit is apt to get large, which is not appropriate for derivingcompactness. Moreover, that is not appropriate either for securing asufficient back focus since a lens unit on the most magnification sidehas a positive refractive power. Furthermore, the zoom optical systemassumes a light source with single wavelength, and is inappropriate fora projection display of a color image.

In addition, in the zoom optical system disclosed in Japanese PatentApplication Laid-Open No. 2002-055279, a synthesized refractive power ofthe adjacent lens units get occasionally negative, that is, therefractive power is weak. Accordingly, the focal length is large as longas 190 mm at minimum. This takes place since the zoom optical system isan optical system intended to be appropriate for an exposure apparatus,and this system is not suitable for an optical system such as aprojector etc. that is desired to derive compactness and a wide angle.In addition, likewise the zoom optical system disclosed in JapanesePatent Application Laid-Open No. 2002-207167, this zoom optical systemassumes a light source with a single wavelength, and therefore isinappropriate for a projecting display of a color image.

SUMMARY OF THE INVENTION

According to one aspect of the invention, a zoom optical systemincludes, in order from a reduction side to a magnification side: afirst lens unit having a positive optical power; a second lens unithaving a negative optical power; a third lens unit having a positiveoptical power; and a fourth lens unit having a positive optical power,wherein respective intervals between the first, second, third and fourthlens units vary during zooming, a magnification-side conjugate positionwith respect to a reduction-side conjugate position and a position of apupil of the zoom optical system with respect to the reduction-sideconjugate position are substantially immobile respectively across anentire zooming range, and the fourth lens unit moves toward themagnification side and an interval between the first lens unit and thefourth lens unit increases during zooming from a wide-angle end to atelephoto end.

According to another aspect of the invention, a projecting opticalsystem includes: a zoom optical system set out in the foregoing, whereina light beam from an original arranged in said reduction conjugateposition is projected onto a surface to be projected.

According to another aspect of the invention, a projecting opticalsystem includes: a zoom optical system set out in the foregoing; areflecting member, substantially arranged in said pupil position, forreflecting light beam from the zoom optical system; and a reflectingoptical system including a plurality of reflecting surfaces forsequentially reflecting light beam from said reflecting member, whereina light beam, which is from an original arranged in said reductionconjugate position and is incident to said zoom optical system, isprojected onto a surface to be projected by said reflecting opticalsystem, and wherein said reflecting member rotates so that a projectedimage projected onto said surface to be projected moves on said surfaceto be projected.

According to another aspect of the invention, an image projectingapparatus includes: a projecting optical system set out in the foregoingand an image forming element of forming said original.

According to another aspect of the invention, an image projecting systemincludes: the image projecting apparatus set out in the foregoing and animage information providing apparatus for supplying said imageprojection apparatus with image information for forming said original.

According to another aspect of the invention, a zoom optical systemincludes in order from a reduction side to a magnification side: a firstlens unit having a positive optical power; a second lens unit having anegative optical power; and a third lens unit having a positive opticalpower, wherein respective intervals between said first, second and thirdlens units vary during zooming, a magnification-side conjugate positionwith respect to a reduction-side conjugate position and a position of apupil of said zoom optical system with respect to a reduction-sideconjugate position are substantially immobile respectively across aentire zooming range, said third lens unit approaches a pupil and aninterval between said first lens unit and said third lens unit increasesduring zooming from a wide-angle end to a telephoto end, and said secondlens unit is configured, in order from said reduction side to amagnification side, by a 2a-th lens sub unit having a negative opticalpower and a 2b-th lens sub unit having a positive optical power.

According to another aspect of the invention, a projecting opticalsystem includes: a zoom optical system set out in the foregoing, whereina light beam from an original arranged in said reduction conjugateposition is projected onto a surface to be projected.

According to another aspect of the invention, a projecting opticalsystem includes: a zoom optical system set out in the foregoing; areflecting member, substantially arranged in said pupil position, forreflecting light from the zoom optical system; and a reflecting opticalsystem including a plurality of reflecting surfaces for sequentiallyreflecting light from said reflecting member, wherein a light beam,which is from--an original arranged in said reduction conjugate positionand is incident to said zoom optical system, is projected onto a surfaceto be projected by said reflecting optical system, and said reflectingmember rotates so that a projected image projected onto said surface tobe projected moves on said surface to be projected.

According to another aspect of the invention, an image projectingapparatus includes: a projecting optical system set out in the foregoingand an image forming element of forming said original.

According to another aspect of the invention, an image projecting systemincludes: the image projecting apparatus set out in the foregoing and animage information providing apparatus for supplying said imageprojection apparatus with image information for forming said original.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing a configuration of a zoom opticalsystem being an embodiment of the present invention;

FIG. 2A is a sectional diagram of a zoom optical system being Embodiment1 of the present invention;

FIG. 2B is a sectional diagram of a zoom optical system of Embodiment 1;

FIG. 3A is a sectional diagram of a zoom optical system being Embodiment2 of the present invention;

FIG. 3B is a sectional diagram of a zoom optical system of Embodiment 2;

FIG. 4 shows a paraxial relationship of a zoom optical system of thepresent invention;

FIG. 5 is a diagram showing a principle of changing a projectingdirection in an image projecting apparatus for which a zoom opticalsystem of Embodiment 1 is used;

FIG. 6 is a sectional diagram showing an image projecting apparatus ofEmbodiment 1 and a projecting optical system used therein;

FIG. 7 is a longitudinal aberration graph of Numerical Embodiment 1 ofthe present invention;

FIG. 8 is a longitudinal aberration graph of Numerical Embodiment 2 ofthe present invention;

FIG. 9 is a graph showing relationships of positions of an object sideprincipal point, an image side principal point and an exit pupil ofNumerical Embodiment 1;

FIG. 10 is a graph showing theoretical values and actual values of theprincipal point intervals of Numerical Embodiment 1;

FIG. 11 is a graph showing relationships of positions of an object sideprincipal point, an image side principal point and an exit pupil ofNumerical Embodiment 2;

FIG. 12 is a graph showing theoretical values and actual values of theprincipal point intervals of Numerical Embodiment 2;

FIG. 13 is a table showing refractive powers of respective units ofNumerical Embodiments 1 and 2; and

FIG. 14 is a drawing of comparing a prior art and the present embodimentin loci of movements of respective lens units during zooming from a wideangle end to a telephoto end.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

An object of the present embodiment is to provide a zoom optical systemthat is not only excellent in telecentricity at the object side andexcellent in invariance of positions of the object surface, the imageplane and the exit pupil to a variation of the focal length but also iscompact and bright and can secure a back focus sufficiently.

Here at first, characteristics of a zoom optical system of the presentembodiment will be described.

One of zoom optical systems of the present embodiment has a plurality ofzoom lens units, that move integrally respectively including, in orderfrom the reduction side to the magnification side, a first lens unithaving a positive optical power, a second lens unit having a negativeoptical power, a third lens unit having a positive optical power and afourth lens unit having a positive optical power. In addition, anotherzoom optical system of the present embodiment has a plurality of zoomlens units that move integrally respectively including, in order fromthe reduction side to the magnification side, a first lens unit having apositive optical power, a second lens unit having a negative opticalpower and a third lens unit having a positive optical power. Of course,other optical elements may be included complementarily. For example, anelement selected from the group consisting of a polarizing plate, awavelength plate, a lens with a weak optical power (refractive power)(that is, a focal length of a wide angle end or a focal length twicelonger than that), a diffraction grating, mirror and the like, thatmight be added to a zoom optical system of the present invention,derives substantially the same zoom optical system of the presentinvention.

And, respective lens units are moved so that intervals betweenrespective lens units vary during zooming, and positions of conjugatepoints on a magnification side as well as a reduction side and a pupilbetween those conjugate points get substantially immobile across theentire zooming range. Moreover, during zooming from the wide angle endto the telephoto end, a lens unit on the most magnification side (thefourth lens unit or the third lens unit) among the magnification lensunits approaches a pupil on the magnification side and an intervalbetween the first lens unit and the lens unit at the most magnificationside increases.

Here, in the present invention, the above described pupil is locatedoutside the zoom optical system. FIG. 1 shows a relationship between aposition of a zoom optical system and a position of an entrance pupil aswell as an exit pupil of the zoom optical system. Both of the pupils arenot present between (inside the range from) the first plane and the lastplane and are located outside.

A first feature is that the first lens unit on the most reduction sideis caused to have a positive refractive power (optical power, that is,an inverse of the focal length) in order to keep the entire zoom opticalsystem compact, secure a sufficient back focus and derive a brightoptical system. Thereby, while restraining the effective diameter of thelens unit arranged on the magnification side of the first lens unit, theNA (numerical aperture) at the object side can be made large.

In the case where the refractive power of the first lens unit isnegative, the effective diameters of the second lens unit and thereafterare apt to get large. Even if the second lens unit is caused to have apositive refractive power, the effective diameter will end in undergoingmagnification as well if an interval between the first lens unit and thesecond lens unit is widened at last when varying focal length,consequently being followed by size increase of the zoom optical systemin its entirety.

A second feature is that, at the time of varying the focal length of azoom optical system from a short side to a long side, that is, duringzooming from a wide end (wide angle end) to a telephoto end (telephotoend), an interval of the lens unit (first lens unit) located at the mostreduction side and the lens unit (fourth lens unit or third lens unit)located at the most magnification side is widened. In case of making thepupil diameter constant to variation of focal length, the NA at thereduction side is maximum with the minimum focal length (wide angle end)and get smaller as the focal length gets longer. Therefore, at the wideangle end, the lens unit located at the most magnification side iscaused to be located at the most reduction side within its mobile range,and be caused to move toward the magnification side as the focal lengthgets longer. Thereby, without making the effective diameter large, highmagnification will be-able to be derived.

A third feature is that in order to keep, across the entire zoomingrange, the position of the object surface (reduction-side conjugatepoint), the image plane (magnification-side conjugate point) and thepupil position substantially constant (immobile) and correct theaberration well, the lens unit arranged between the lens unit located atthe most reduction side and the lens unit located at the mostmagnification side is also made mobile.

Here, when increasing the number of movable lens units, the aberrationcan be corrected better, but the present invention will not limit thenumber of mobile lens units. Moreover, addition of a focus lens unitthat does not substantially attribute to zooming increases the number ofmobile lens units, and this case is also included in the scope of thepresent invention.

A fourth feature is that the position, at the telephoto end, of the lensunit located at the most reduction side is closer to the reduction-sideconjugate plane (conjugate point) than the position, at the wide angleend, of the lens unit located at the most reduction side is, and theposition, at the telephoto end, of the lens unit located at the mostmagnification side is closer to the magnification-side conjugate planethan the position, at the wide angle end, of the lens unit located atthe most magnification side is. Thereby, high magnification in spite ofcompactness is derived.

In case of taking the reduction-side conjugate plane as the objectsurface, the magnification-side conjugate plane becomes the image plane,the reduction side pupil becomes the entrance pupil and themagnification side pupil becomes the exit pupil. FIG. 14 schematicallyshows that, during zooming from the wide angle end to the telephoto end,the movable lens units move along different loci. Reference character LVdenotes an object surface where a light bulb (liquid crystal displaypanel) is disposed in an image projecting apparatus described later.Reference characters G1 to G4 denote a first to a fourth lens unit,reference character BF denotes a back focus, reference character EPdenotes an exit pupil, reference character SP denotes a space at anobject side, reference character ESP denotes a space at an exit pupilside, reference character fw denotes a focal length at a wide angle endand reference character ft denotes a focal length at a telephoto end.

As in Type A where the first lens unit G1 at the most object side movestoward the image side (exit pupil side) as the focal length gets longer,an advantageous use of the space SP on the object side will not befeasible during zooming implemented by enlarging an interval between thefirst lens unit G1 and the third lens unit G3, and in order to derivehigh magnification, the total length of the zoom optical system will getlong.

In contrast, in zooming in case of Type B corresponding to the presentembodiment, as the focal length gets long, the first lens unit G1approaches the object surface and moreover the third lens unit G3 movesin the opposite direction of the first lens unit G1. Thereby, the spaceSP is utilized effectively to enable an interval between the first lensunit G1 and the third lens unit G3 to be widened more easily than inType A and to enable the zoom optical system to get compacter than inType A in case of deriving the same magnification. Moreover, inEmbodiment 1 to be described later, the fourth lens unit G4 moves so asto sufficiently secure the space ESP where a rotational mirror (RM inFIG. 5) is arranged. In addition, in case of Embodiment 2, with thespace ESP having been secured, the third lens unit G3 moves in theopposite direction of the first lens unit G1.

A fifth feature is that the optical system is substantially telecentricon the object side and a plurality of lens units are moved along therespective loci determined so that, across entire zooming range,distance from image side principal point to the exit pupil of the zoomoptical system becomes substantially equal to the focal length of thezoom optical system.

In addition, in this relation, a seventh feature is that a plurality oflens units are caused to move along the respective loci determined sothat the interval between the object side principal point of the zoomoptical system and the image side principal point becomes substantiallyequal toE−fz−fz(x′+fz)/x′  (1)where E represents the distance from the object surface to the exitpupil surface located between the object surface and the image plane ofthe zoom optical system, x′ represents the distance from the exit pupilsurface to the image plane and fz represents the focal length of thezoom optical system. Here, the description “become/be substantiallyequal to” is adopted, and this description means that discrepancy up to5% (preferably 3% and more preferably 1%) from the value of the abovedescribed conditional Expression (1) is tolerant.

Here, FIG. 4 shows a paraxial relationship of a zoom optical system ofthe present embodiment. In case of taking the reduction-side conjugateplane as the object surface, in a state of the object side beingtelecentric, the exit pupil is derived in the position apart from theimage side principal point at a distance equivalent to the focal lengthfz of the zoom optical system. That is, as concerns arrangements of lensunits in the zoom optical system of the present embodiment and the lociof movement thereof, across the entire zooming range, the image sideprincipal point is set to be located to the object side at a distance ofonly the focal length fz in that magnification state apart from apredetermined exit pupil position (fifth feature).

Respectively for Embodiment 1 and Embodiment 2, FIG. 9 and FIG. 11 showdistance from the image side principal point to the exit pupil. Fromthese drawings, it is apparent that distance from the image sideprincipal point to the exit pupil is substantially equal to the focallength of the zoom optical system.

In addition, the image side principal point is set so as to derive apredetermined magnification, in addition to relationship with the exitpupil position, in a state that the object surface and the image planeare in predetermined positions during zooming.

That is, ideally, if the lens units are arranged so that the image sideprincipal point is located to the object side at only distance apartequivalent to the focal length fz from the exit pupil position, andmoreover an interval between the object side principal point and theimage side principal point (H′z-Hz) is substantially equal to the valueof the above described expression (1), in a telecentric optical system,positions of the object surface, the image plane, the entrance pupil(infinity) and the exit pupil can be made constant (immobile) duringzooming (sixth feature).

Respectively for Embodiment 1 and Embodiment 2, in FIG. 10 and FIG. 12,theoretical values of the Expression (1) is indicated with a solid lineand the actual principal point interval with each focal length derivedby dividing the range of the focal length equally by five is plottedwith void marks. From these drawings, it is apparent that the intervalbetween the object side principal point and the image side principalpoint is substantially equivalent to the values of the Expression (1).

A seventh feature is that, across the entire zooming range, distancefrom an object surface to the first lens unit (back focus) is threetimes or more larger than the maximum object height. In a 3-plate typeimage projecting apparatus to be described later, in order to arrangecolor synthesizing member for synthesizing three color lights of red,green and blue on the reduction side of the zoom optical system, withthe back focus being 3 times or more larger than the maximum objectheight (that refers to the distance from the point at the distance fromoptical axis being farthest among effective areas of image formingapparatus such as a crystal display panel etc. arranged in thereduction-side conjugate position to the optical axis.), the space (SPin FIG. 14) where the color synthesizing member is arranged can besecured.

An eighth feature is that, across the entire zooming range, the intervalbetween the pupil on the magnification side and the lens unit located atthe most magnification side of the zoom optical system is longer than ahalf of the minimum diameter of the pupil on the magnification side(multiplied by preferably 1 and more preferably by 2).

FIGS. 2B and 3B are sectional diagrams showing Embodiments 1 and 2including the minimum diameter of the pupil on the magnification side.As apparent from these drawings, across the entire zooming range betweenthe telephoto end and the wide angle end, an interval between the pupilon the magnification side and the lens unit located at the mostmagnification side (the fourth lens unit G4 in Embodiment 1 and thethird lens unit G3 in Embodiment 2), that is, the space ESP shown inFIG. 14, is secured wider than the minimum diameter (of course widerthan a half of the minimum diameter) of the pupil on the magnificationside.

Thereby, for example, as embodiments to be described later, in case ofarranging a rotatable mirror (RM in FIG. 4) in the position of the exitpupil, interference between the mirror and the lens unit located at themost magnification side can be avoided. Here, actually, since a drivemechanism of the mirror is present around the mirror, it is necessary towiden the above described distance to a certain extent than a half ofthe minimum diameter of the exit pupil, but it is advisable to setwithin 10% of the distance (conjugate length) between the object surfaceand the image plane (conjugate points on the reduction side as well ason the magnification side). In addition, setting of “the minimumdiameter of the pupil” is intended for application in case of differentpupil diameters in two mutually perpendicular directions on the pupilplane as well. Here, the minimum diameter of the pupil is the diameterof the inscribed circle of the external shape of the pupil.

Here, as another feature, in the present embodiment, employingaspherical surface for the zoom optical system, aberrations arecorrected well. The zoom optical system of the present embodiment iscompact, derives high magnification, and simultaneously, unlike the zoomoptical systems for an exposure apparatus having been disclosed inJapanese Patent Application Laid-Open No. 2002-207167 and JapanesePatent Application Laid-Open No. 2002-055279, is suitable for an opticalapparatus that requires a wide-angle optical system such as a projectoretc. with the focal length at the wide angle end being smaller than thezoom optical systems in Japanese Patent Application Laid-Open No.2002-207167 and Japanese Patent Application Laid-Open No. 2002-055279.Therefore, due to a large refractive power that the zoom optical systemhas, simultaneous correction of the spherical aberration and thechromatic aberration across the entire zooming range will becomedifficult. The reason hereof is that the chromatic aberration arisessignificantly due to a strong positive refractive power of the entireoptical system, and it becomes more difficult to correct the chromaticaberration while correcting the spherical aberration than in an opticalsystem with the refractive power being comparatively weak.

Therefore, in the present embodiment, with compactness being maintained,aspherical surface is used in order to correct the chromatic aberration,and the spherical aberration is corrected with degrees of freedom of theshape taken by the aspherical surface. In particular, employment of theaspherical surface that has a large diameter gives rise to a largeaberration correction effect. Embodiments 1 and 2 are shown with thezoom optical system that has utilized the aspherical surface.

Embodiment 1

FIG. 5 shows an image projecting apparatus comprising a projectingoptical system subject to combination of a zoom optical system of anembodiment of the present invention and an Off-Axial optical system.Here, the Off-Axial optical system is defined as an optical systemincluding a curved surface (Off-Axial curved surface) with a normal tothe surface at the intersection between the reference axis and theconfiguring surface being not present on the reference axis where thereference axis is defined as the route traced by a light beam thatpasses the image center and the pupil center. In this case, thereference axis will be in a bent shape. Making the configuring surfacesof the optical system asymmetrical and aspherical, an optical systemthat has sufficiently undergone correction of the aberration can beconfigured (see Japanese Patent Application Laid-Open No. H09-005650,Japanese Patent Application Laid-Open No. H08-292371, Japanese PatentApplication Laid-Open No. H08-292372 and Japanese Patent ApplicationLaid-Open No. H09-222561).

In addition, in this Off-Axial optical system, the constituent surfaceswill be generally not co-axial, vignetting does not arise even on areflecting surface and therefore an optical system with a reflectingsurface is easily established. In addition, forming an intermediateimage in the optical system, an optical system that has a wide viewangle and is nevertheless compact can be configured. Moreover, such anoptical system can be configured that is an optical system with thefront stop and is nevertheless compact since the optical path can bedesigned comparatively freely.

In the present embodiment, employing such an Off-Axial optical system, aprojecting optical system with a wide view angle, high fineness and highmagnification can be realized, and moreover employing such a zoomoptical system of the present embodiment and rotating a flat surfacemirror to be described later, it will become possible to movesignificantly or incline (that is, vary the projecting angle) theposition of the projected image with less deterioration in imagequality.

Here, a basic principle for varying the projection angle while keepinggood optical performance will be described with reference to FIG. 5.

In FIG. 5, reference character LL denotes an image forming element suchas a liquid crystal panel etc. and an illumination system for radiatinglight modulated by the image forming element. Reference character Cdenotes an optical block having the image forming capability. The lightemitted from the illumination system and having undergone modulation bythe image forming element is reflected by a rotatable flat surfacemirror RM and thereafter undergoes image forming into the area B1 of thespherical surface E′ with the position of the exit pupil EP of the firstoptical block C being the center of curvature. Here, it is advisablethat the first optical block C is capable of image forming on the curvedsurface area B1, and therefore it may be an optical block of co-axiallyrotational symmetry or may be an optical block including a reflectingsurface having curvature as a constituent. However, in the presentembodiment, the first optical block C is configured by a zoom opticalsystem related to the present invention.

Moreover a flat surface mirror RM arranged in the position of the exitpupil EP is caused to rotate on the sheet surface of FIG. 5, and thenthe image formed in the area B1 moves to the areas A1 or C1 on thespherical surface E′, accompanying few optical changes. That is, theimage moves in a continuous fashion on the spherical surface E′ withstill retaining the state of image forming.

Thus the light reflected by the flat surface mirror RM is lead to asecond optical block R as an Off-Axial optical system with a pluralityof reflecting surfaces with curvature as constituent. At this time, thesecond optical block R is designed to bring an image on the sphericalsurface E′ into image forming onto a screen E with good opticalcapability. Moreover characteristics of the Off-Axial optical systemenable an image to be obliquely projected to the screen E withoutcausing any image distortion to arise.

Accordingly, in a sate of the flat surface mirrors RM rotating in theposition to direct the light to the area B1, an image of the originalformed on the image forming element is displayed in the area B2 on thescreen E via the first optical block C, the flat surface mirror RM andthe second optical block R.

In addition, rotating the flat surface mirror RM, images formed in theareas A1, B1 and C1 on the spherical surface E′ can be formed in theareas A2, B2 and C2 on the screen E. That is, the image can be projectedwith any projecting angle onto the range (screen E) that the secondoptical block R secures good optical performance. However, the memberrotating around the exit pupil EP of the first optical block C as thecenter will not be limited to the flat surface mirror RM, but the firstoptical block C and the image forming element may be caused to rotateintegrally, or the second optical block R may be rotated. As these arerelative rotation of the above described optical block, rotation of anyoptical block is optically equivalent.

Moreover in the area B1 on the spherical surface E′, image forming doesnot always have to take place on the spherical surface. That is, thespherical surface E′ does not have to be a spherical surface. In otherwords, in order to make the projecting angle variable, the image of thefirst optical block C is required to move in a continuous fashion withgood optical characteristics being kept, and in order to realize itideally, the surface E′ is desired to be a spherical surface. However,actually, since tolerance of the optical characteristics such as focaldepth, distortion and the like is limited within a range, in case offalling within this tolerance, surface E′ may have any surface shape,and does not necessarily have to be a spherical surface. Here,positional accuracy of the flat surface mirror RM arranged in theposition of the exit pupil does not have to strictly correspond to theposition of the exit pupil of the first optical block C, and it isadvisable that correspondence is implemented within a range of toleranceto a certain extent.

Moreover, the image forming capability of the first optical block C willbe described further in detail. In case of making an image plane Smovable two-dimensionally on a screen E by a projecting optical systemof the present embodiment, as long as the aberration of entire angle ofview arises uniformly respectively in each azimuth direction, theaberration does not have to undergo sufficient correction. The reasonthereof is that, if the aberration of entire angle of view arisesuniformly, correction can be derived by the second optical block Rconfigured by a reflecting surface having a curvature.

In addition, in case of making a position of the image plane S movableonly in the one-dimensional direction on the screen E, as long as theaberration of entire angle of view arises uniformly only in the mobiledirection, an image forming performance in the direction different fromthe moving direction does not have to be good. The reason thereof isalso that the second optical block R can implement correction.

Here, only the principle about movement of the image plane on the sheetsurface in FIG. 5 was described, but this is likewise applicable to thecase where the image plane is moved in the direction perpendicular tothe sheet surface. However, a member of rotating around the exit pupilEP of the first optical block C as a center is only a flat surfacemirror RM, in the case where the image plane is moved two-dimensionallyon the screen E, it is advisable that a flat surface mirror in charge ofrotation in the horizontal direction and a flat surface mirror in chargeof the vertical direction are used. The reason thereof is that, in FIG.5, when the flat surface mirror RM is caused to rotate in the directionperpendicular to the sheet surface in the drawing, the image formingelement and the flat surface mirror RM will be disposed to derive atwisted relationship, a light beam on the reference axis on the screen Eundergoes image forming onto a desired location, but the image plane Srotates on the screen E.

However, it is physically impossible to arrange a plurality of flatsurface mirrors onto the exit pupil EP of the first optical block C.Therefore, even if the flat surface mirror RM is not strictly disposedin the position of the exit pupil EP, the image on the spherical surfaceE′ falls within the range of tolerance of optical performance, two flatsurface mirrors RM can be arranged in the vicinity of the exit pupil EPsubject to displacement to such a degree that will not cause mutualinterference.

Next, the case where the zooming is implemented in these projectingoptical system and image projecting apparatus will be described. If thefirst optical block C is caused to have zooming function to vary thesize of the image formed in the areas A1, B1 and C1 on the sphericalsurface E′ formed by the first optical block C, it is possible to varythe size of the image formed in the areas A2, B2 and C2 on the actualimage plane (screen) E.

However, based on the description on the above described principle, inorder to rotate the mirror RM in the position of an exit pupil EP of thefirst optical block C, the position of the exit pupil EP is desired tobe kept always constant during zooming. With the position of the exitpupil EP being constant, the mirror RM and the second optical block Rcan be arranged in fixed positions.

In a normal camera lens, the object surface and the image plane arerequired not to vary in position regardless of focal length varyingcontinuously, and in addition hereto, the first optical block C of thepresent embodiment, that is, the zoom optical system related to thepresent invention is required that positions of the entrance pupil andthe exit pupil are kept constant regardless of variation of the focallength. Here, the reason why the position of the exit pupil is requiredto be constant is as described in the above described principle, but asconcerns the position of the entrance pupil, that the telecentricity isrequired in the case where a liquid crystal panel is used as an imageforming element.

As follows, in a 3-plate type image projecting apparatus whichsynthesizes the red, green and blue modulated lights to enter the firstoptical block C, a further specific configuration of a zoom opticalsystem that secures a sufficient space (that is, the back focus of thefirst optical block C) for inserting color synthesizing elements etc.between the image-forming element and the first optical block C (zoomoptical system), that is excellent in telecentricity on the object sideand that is excellent in the immobility of the positions of the objectsurface, the image plane, the entrance pupil and the exit pupil tovariation of the focal length will be described.

FIG. 6 shows an entire configuration of a 3-plate type image projectingapparatus. In FIG. 6, reference character LO denotes an illuminatingsystem, which has a white light source lamp 1, a reflecting mirror 2, a(not shown) color splitting element of splitting the white light fromthe light source lamp 1 into components of three colors of red, greenand blue.

Reference character LV denotes a liquid crystal display panel of atransparent type as an image forming element. To this liquid crystaldisplay panel LV a drive circuit 10 is connected. An image informationproviding apparatus 20 such as a personal computer, a DVD player, avideo (VCR), a television, a digital video or a still camera and areception unit consisting of an antenna of receiving images in radiowaves and a tuner etc. is connected to the drive circuit 10. The drivecircuit 10 in reception of image information from the image informationproviding apparatus 20 delivers a drive signal corresponding with theimage information to the liquid crystal display panel LV. The liquidcrystal display panel LV in reception of the drive signal forms anoriginal corresponding with the drive signal to modulate theilluminating light from the illuminating system LO. The presentembodiment is provided with three liquid crystal display panels LVrespectively for red, green and blue, which are not shown though, toform originals for red, green and blue.

Here, in the present embodiment, the case where a liquid crystal displaypanel of a transparent type is used as an image forming unit isdescribed, but the present invention will not be limited thereto, but isapplicable to the case where a liquid crystal display panel of areflection type and a digital micro mirror array (DMD) are used and tothe case where a self-luminous element (electroluminescence element)that does not require any illumination system is used.

Reference character D denotes a dichroic prism as a color synthesizingelement for synthesizing color light modulated with three liquid crystaldisplay panels LV. Dichroic prism D is provided with a plurality ofdichroic films to synthesize three color lights with transparent orreflecting operation corresponding with wavelength at these dichroicfilms. FIG. 6 shows two dichroic prisms, and it is advisable that thisis varied in accordance with what the image forming element LV requires.In addition, instead of a dichroic prism, a polarizing beam splitter maybe used.

Reference character C denotes a zoom optical system configuring thefirst optical block in FIG. 5, and a refractive optical unit(hereinafter to be referred to as “first refractive optical unit”)configured as a coaxial optical system by a plurality of lens units.Reference characters EP denotes an exit pupil of the zoom opticalsystem, and also an entrance pupil of the reflecting optical unit R as asecond optical block being an Off-Axial optical system configured by aplurality of reflecting surfaces R1 to R4. Here, in this position or inthe vicinity of this position, a stop may be provided in accordance withnecessity.

The light subject to color synchronization with the dichroic prism Dtravels via a first refractive optical unit C, a first flat surfacemirror RM that can rotate at the position of the exit pupil EP andreflecting optical units (R1 to R4) and moreover, via the second flatsurface mirror TM and the second refractive optical unit C2, is enlargedand projected onto a not shown screen being a surface to be projected.Here, this second refractive optical unit C2 is configured by a cementedlens consisting of one negative lens (negative meniscus lens shapedconvex to the reduction conjugate side) and one positive lens (biconvexlens), but is not limited thereto. Of course, not a cemented lens but anegative lens and a positive lens may be arranged at an interval, or abiconcave lens and a biconvex lens may be used for configuration, or anegative meniscus lens being convex to the magnification conjugate sideand a positive meniscus lens likewise being convex to the magnificationconjugate side may be cemented. In addition, only one positive lens(desirably a positive lens being convex to the magnification conjugateside) or one negative lens may be used for configuration. However,preferably the number of refractive optical elements disposed on theprojected surface side of the reflecting optical system is preferablynot more than 4.

In addition, the projecting optical system configured by the first andthe second refractive optical units C and C2, the first and the secondflat surface mirrors RM and TM and moreover a reflecting optical unit Rcorrects trapezoidal distortion well by the reflecting optical unit R asan Off-Axial optical system and obliquely projects an image onto thescreen.

In addition, causing the projecting optical system to include the firstrefractive optical unit C, the first refractive optical unit C and thereflecting optical unit R can be appropriately assigned to take sharedcharge of the optical power required for enlarging/projection onto thescreen. Therefore, curvature of each reflecting surface of thereflecting optical unit R is made moderate so that manufacturing can bemade simple and the sensibility to manufacturing errors can be reduced.Here, an influence of astigmatism difference etc. due to manufacturingerrors of the reflecting surface become large on the surface closer to apupil. In addition, astigmatism difference etc. having arisen on thefirst reflecting surface closest to the exit pupil EP among a pluralityof reflecting surfaces are magnified in accordance with magnification ofthis reflecting optical unit. Accordingly, sensibility of the reflectingoptical system can be reduced by sharing assignment of magnification(optical power) required for image projection with a refractive opticalsystem being low in sensibility susceptible to capability deteriorationdue to manufacturing errors compared with a reflecting optical system.

Moreover, even in case of projecting optical system being of wide angle,setting focal length of the first refractive optical unit C long,occurrence of a magnification chromatic aberration will be restrainedcomparatively easily. A chromatic aberration does not arise in thereflecting optical unit R, that is effective for correction on therespective aberrations.

In FIG. 6, any of the reflecting surfaces R1 to R4 (all of thesereflecting surfaces R1 to R4 have optical power) configuring areflecting optical unit R is in rotational asymmetrical shape andconfigures the Off-Axial optical system with reference axis being bentas described above.

Moreover, the present embodiment undergoes intermediate image formingonce (intermediate image forming surface M) between the reflectingsurfaces R3 and R4 in the reflecting optical unit R (a surface, that isconjugate to both of the liquid crystal display panel and the screen, isformed between R3 and R4 in the reflecting optical units). Thereby,compared with the case of absence of an intermediate image formingsurface, the size of each reflecting surface can be made small, which istherefore effective in manufacturing the surface face accurately. Here,the position of the intermediate image forming surface will not belimited to the position shown in FIG. 6. In the present embodiment, thereflecting optical unit R includes four reflecting surface havingoptical powers, but will not be limited thereto, and any number ofplanes, nevertheless, being two or more planes (preferably 3 planes ormore), will do. Among them, if the zoom optical system is configured sothat the intermediate image is formed between the reflecting surface atthe most screen side and the second reflecting surface from the mostscreen side, the size of each reflecting surface can be made small.

Accordingly, according to the principle of varying the projection angledescribed with reference to FIG. 5 in the projecting optical systemshown in FIG. 6, the projecting angle of an image from the projectingoptical system can be changed by rotating the first flat surface mirrorRM.

The zoom optical system of the present embodiment secures a sufficientspace for inserting color synthesizing elements etc., is excellent intelecentricity on the object side, is excellent in the immobility of thepositions of the object surface, the image plane and the exit pupil tovariation of the focal length, secures a space for arranging a rotatablemirror between a lens unit closest to the exit pupil and the exit pupilposition and is suitable to an Off-Axial optical system having thefunction of moving the image plane and an image projecting apparatususing the same.

The zoom optical system of the present Embodiment 1 and Embodiment 2 tobe described later corresponds with the zoom partial system of theprojecting optical system with the liquid crystal panel size being 0.7inch and the aspect ratio 4:3.

FIG. 2A and FIG. 2B show respectively X-Z sectional views as well as Y-Zsectional views of configurations of a zoom optical system configuringthe first refractive optical unit C. As described above, this zoomoptical system is used as a partial system configuring a part of theprojecting optical system. Here, in this drawing, reference charactersLV, D and EP denote the same constituents as the reference characters inFIG. 6 do.

FIG. 2A and FIG. 2B, the zoom optical system is configured, in orderfrom the reduction side to the magnification side (in the presentembodiment, from the liquid crystal display panel LV side being theobject side to the spherical surface area B1 side being image side:hereinafter reference character B1 is referred to as an image plane), bya first lens unit G1 having a positive refractive power, a second lensunit G2 having a negative refractive power, a third lens unit having apositive refractive power and a fourth lens unit having a positiverefractive power. The first to fourth lens units G1 to G4 respectivelymove integrally along the optical axis AXL during zooming (varying thefocal length) so that intervals between respective lens units vary.

In addition, this zoom optical system is always substantiallytelecentric on the object side under the all focal length states, thatis, in the entire zooming range, between the maximum focal length(telephoto end) and the minimum focal length (wide angle end), and theposition of the exit pupil EP located between the fourth lens unit G4and the image plane B1, the position of the reduction-side conjugatepoint where the liquid crystal display panel LV is arranged and theposition of the magnification-side conjugate point where the image planeB1 is located are substantially immobile respectively.

Here, “the position of the image plane B1 (the position ofmagnification-side conjugate point) is immobile” means that the positionof this image plane B1 and the position of the liquid crystal displaypanel (the position of reduction-side conjugate point) remainsubstantially unchanged. Specifically, the distance between theconjugate point of the liquid crystal display panel formed by theoptical system (including the first refractive optical unit C) arrangedbetween this liquid crystal display panel and the exit pupil and theliquid crystal display panel (the distance on the optical path of thelight beam passing the optical axis of the first refractive opticalunit) changes only as much as 5% (preferably 3% and more preferably 1%)in the entire zooming range (from the wide angle end to the telephotoend). The phrase “the distance changes” quoted here means that theminimum value of the distance within the entire zooming range is presentwithin the range of discrepancy not more than 5% of the maximum value tothe maximum value (that is, the maximum value×0.95≦the minimum value).

The position of the exit pupil is likewise, and it is meant that theposition of the exit pupil is immobile with respect to the position of aliquid crystal display panel. In addition, the minimum value in theentire zooming range of the distance between the exit pupil and theliquid crystal display panel is not less than 95% (preferably not lessthan 97% and more preferably not less than 99%) of the maximum value.

Here, in particular the position of the exit pupil EP being“substantially immobile” means that displacement of 2 to 3% andpreferably up to 1% of the distance between the magnification-sideconjugate point and the reduction-side conjugate point is tolerant. Thereason hereof is that a range of tolerance of the opticalcharacteristics such as the focal depth or distortion etc. is, actually,present as described above.

In addition, in the zoom optical system, during zooming from the wideangle end to the telephoto end, the interval between the first lens unitG1 and the second lens unit G2 increases monotonously while the intervalbetween the second lens unit G2 and the third lens unit G3 decreasesmonotonously. In addition, the interval between the third lens unit G3and the fourth lens unit G4 increases monotonously. That is, theinterval between the first lens unit G1 and the second lens unit G2 atthe telephoto end is wider than that at the wide angle end, the intervalbetween the second lens unit G2 and the third lens unit G3 at thetelephoto end is narrower than that at the wide angle end and theinterval between the third lens unit G3 and the fourth lens unit G4 atthe telephoto end is wider than that at the wide angle end. And, duringzooming from the wide angle end to the telephoto end, the intervalbetween the first lens unit G1 and the fourth lens unit G4 increases.

In addition, the position of the first lens unit G1 at the telephoto endis closer to the reduction side conjugate point (LV) than the positionof the first lens unit G1 at the wide angle end is while the position ofthe fourth lens unit G4 at the wide angle end is closer to themagnification side conjugate point (B1) than the position of the fourthlens unit G4 at the wide angle end is Providing an additional account,during zooming from the wide angle end to the telephoto end, the fourthlens unit G4 approaches the pupil EP on the magnification side.

In addition, in the present embodiment, as shown in FIGS. 2A and 2B, therelationship between the width Eo in the Y axis direction of the exitpupil EP and the width Er in the X axis direction will be:Eo<Er,(for example, Er=2Eo). That is, the diameter of the exit pupil EP in theY axis direction is different from that in the X axis direction, and theminimum diameter will be Eo.

In addition, the image B1 in FIG. 2A is able to be moved by rotating theflat surface mirror RM disposed in the position of the exit pupil EP asdescribed in the principle of varying the above described projectingdirection.

In the present Embodiment 1, the first lens unit G1 is caused to have apositive refractive power in order to secure the back focus and derive abright optical system while keeping the entire zoom optical systemcompact.

Hereinafter, as the numerical embodiment 1 corresponding with Embodiment1 shown in FIGS. 2A and 2B, the configuring data of the zoom opticalsystem is shown in Table 1. In Table 1, “surface number” i refers to the“i”-th surface counted from the object side. The “curvature radius”refers to a paraxial curvature radius (mm) of the “i”-th surface, the“surface interval” refers to an interval (mm) between the “i”-th surfaceand the “i+1”-th surface and “refractive index” and “Abbe constant”respectively refer to the refractive index and the Abbe constant of themedium between the “i”-th surface and the “i+1”-th surface. Thesedefinitions will be applicable to the following numerical embodiments.In addition, FIG. 13 shows the refractive power of respective lens unitsin the present numerical embodiment 1.

Moreover, in the present numerical embodiment, respective aberrationsare corrected well by configuring the 14th surface having the maximumdiameter among the zoom optical systems as an aspherical surface.

Here, aspherical surface shape is to be expressed by the followingExpression (2), taking Z axis in the optical axis direction and r axisin the direction perpendicular to the optical axis, and with a travelingdirection of light being positive, with the conic constant being K andthe coefficient of the 4-th to the 10-th deformation being A to D, whileconstants and coefficients in the Expression are indicated in Table 2 ofEmbodiment 2. Here, a set of characters “E-X” denotes “×10^(−x)”. Inaddition, reference character c denotes a curvature of the surfacevertex. $\begin{matrix}{{z(r)} = {\frac{{cr}^{2}}{\sqrt{2 - {\left( {1 + K} \right)c^{2}r^{2}}}} + {Ar}^{4} + {Br}^{6} + {Cr}^{8} + {Dr}^{10}}} & (2)\end{matrix}$ TABLE 1 <<Numerical Embodiment 1>> Liquid crystal panelsize: 0.7 inch (maximum object height of 8.89 mm) Focal length fz: 74.0to 111.0 Zoom ratio: 1.50 Aperture stop diameter: 40.0 mm surface numbercurvature surface object radius interval refractive Abbe surfaceinfinite variable index constant 1 55.4025 4.9816 1.743972 44.8504 2−59.5194 8.3439 3 −57.7241 3 1.521304 54.8272 4 51.6031 variable 570.7295 3.9104 1.741103 45.0751 6 −81.3061 2.1799 7 −25.829 3 1.75520127.5795 8 60.3351 variable 9 303.3369 11.0747 1.541686 65.3084 10−22.9177 0.1 11 −23.0008 3 1.74801 36.5426 12 −45.2477 variable 13−111.1783 7.737 1.687511 47.3584 14 −34.1932 variable (asphericalsurface) 15 infinite 250 16 −250 0 (image plane) Coefficient ofaspherical surface 14-th surface K (conic coefficient): −0.331819A(4-th): −0.652047E−7 B(6-th): −0.302567E−9 C(8-th): −0.105026E−12D(10-th): −0.788268E−16 Variable interval fz 74 83.25 92.5 101.75 111 d049.4452 46.0267 45 45.7361 47.9362 d4 0.4114 9.3065 15.9238 21.064625.15 d8 7.8767 6.926 5.3013 3.2911 1.019 d12 1.6669 5.2116 9.359513.8657 18.5673 d14 43.2724 35.2018 27.088 18.715 10

Here, the back focus (the distance between the first lens unit and thereduction-side conjugate position) in the above described Table 1 willbe not less than 45 (mm) and not more than 49.4452 (mm). This value is avalue derived by the back focus having undergone air conversion, beingdesired to be 35 mm or more (preferably 40 mm or more) across thezooming range. In other words, 45% or more (preferably 50% or more) offocal length at the wide angle end of the zoom optical system ispreferable. Moreover, this back focus is around approximately 5.06 timesto 5.56 times higher than the maximum object height (8.89 mm) across theentire zooming range. This back focus is desired to be three times ormore (preferably four times or more) higher and is desired to be tentimes or less (preferably seven times or less) than the maximum objectheight. These are accountable to the following numerical embodiment 2(back focus length of 45 to 52.4229 mm, and this is around approximately5.06 times to 5.56 times higher than the maximum object height) as well.

In addition, the zoom ratio (the value derived by dividing the focallength at the telephoto end by the focal length at the wide angle end)of the present embodiment is set to 1.50 but will not be limitedthereto. Here, at least 1.2 times or more (preferably 1.3 times or moreand more preferably 1.4 times or more) will do. The upper limit value isdesired to be 3.0 times or less and preferably 2.5 times or less, morepreferably 2.0 times or less. This is also accountable to the followingNumerical Embodiment 2 (magnification proportion of 1.90) as well.

FIG. 9 shows that the interval between the exit pupil and the image sideprincipal point position of the present numerical embodiment 1 issubstantially equal to the focal length of the zoom optical system. Asapparent from this drawing, each lens unit is arranged so that thedistance fz from the image side principal point to the exit pupilsubstantially corresponds to each focal length, and therefore, inaddition to the object surface and the image plane, the exit pupilsurface can be made immobile during zooming.

Moreover, in FIG. 10, theoretical values of Expression (1) is indicatedwith a solid line and the actual principal point interval with eachfocal length derived by dividing the range of the focal length equallyby five is plotted with void marks. From this drawing, it is apparentthat the interval between the object side principal point and the imageside principal point in the present numerical embodiment 1 issubstantially equal to the values of Expression (1).

In addition, longitudinal aberration graphs of the present numericalembodiment 1 are shown in FIG. 7. FIG. 7 shows longitudinal aberrationgraphs in wide angle (74 mm focal length), middle (92.5 mm focal length)and tele (111 mm focal length) in order from the top. The wavelengths ofassessment light beams are 620 nm (red R), 550 nm (green G) and 470 nm(blue B). From this drawing, it is apparent that image forming has beenimplemented well.

Embodiment 2

FIG. 3A and FIG. 3B show respectively X-Z sectional views as well as Y-Zsectional views of configurations of a zoom optical system of Embodiment2 of the present invention which configures the first refractive opticalunit C shown in FIG. 6. This zoom optical system is used as a partialsystem configuring a part of the projecting optical system. Here, inthis drawing, reference characters LV, D and EP denote the sameconstituents as the reference characters in FIG. 6 do.

In FIG. 3A and FIG. 3B, the zoom optical system has, in order from thereduction side to the magnification side (in the present embodiment,from the liquid crystal display panel LV side being the object side tothe spherical surface area B1 side being image side: hereinafterreference character B1 is referred to as an image plane), a first lensunit G1 having a positive refractive power, a second lens unit G2 havinga negative refractive power and a third lens unit having a positiverefractive power.

Here, a second lens unit G2 is configured by two lens units of a 2a-thlens sub unit G2 a having a negative refractive power and a 2b-th lenssub unit G2 b having a positive refractive power, that is, it can beconsidered the zoom optical system is in a 4-lens unit configuration.

The second lens unit consists of three lenses, but first two lenses (5thsurface to 8th surface) in view from the reduction side are a 2a sublens unit and the optical power is negative of −0.0168136. The last onelens (9th surface to 10th surface) is the 2b sub lens unit, the opticalpower is positive of +0.00942778.

The first to third lens units G1 to G3 respectively move integrallyalong the optical axis AXL during zooming (varying the focal length) sothat intervals between respective lens units vary.

In addition, this zoom optical system always is substantiallytelecentric on the object side under the all focal length states, thatis, in the entire zooming range, between the maximum focal length(telephoto end) and the minimum focal length (wide angle end), and theposition of the exit pupil EP located between the third lens unit G3 andthe image plane B1, the position of the reduction-side conjugate pointwhere the liquid crystal display panel LV is arranged and the positionof the magnification-side conjugate point where the image plane B1 islocated are substantially immobile respectively.

In addition, in the zoom optical system, during zooming from the wideangle end to the telephoto end, the interval between the first lens unitG1 and the second lens unit G2 increases monotonously. In addition, theinterval between the second lens unit G2 and the third lens unit G3decreases once from the wide angle end and thereafter increases towardthe telephoto end. That is, the interval between the first lens unit G1and the second lens unit G2 at the telephoto end is wider than theinterval at the wide angle end while the interval between the secondlens unit G2 and the third lens unit G3 at the telephoto end is widerthan the interval at the wide angle end. And, during zooming from thewide angle end to the telephoto end, the interval between the first lensunit G1 and the third lens unit G3 increases monotonously In addition,the position of the first lens unit G1 at the telephoto end is closer tothe reduction side conjugate point (LV) than the position of the firstlens unit G1 at the wide angle end is while the position of the thirdlens unit G3 at the telephoto end is closer to the magnification sideconjugate point (B1) than the position of the third lens unit G3 at thewide angle end is. Providing an additional account, during zooming fromthe wide angle end to the telephoto end, the third lens unit G3approaches the pupil EP on the magnification side.

In addition, in the present embodiment, as shown in FIGS. 3A and 3B, therelationship between the width Eo in the Y axis direction of the exitpupil EP and the width Er in the X axis direction will be:Eo<Er,(for example, Er=2Eo). That is, the diameter of the exit pupil EP in theY axis direction is different from that in the X axis direction, and theminimum diameter will be Eo.

In addition, the image B1 in FIG. 3A is moved by rotating the flatsurface mirror RM disposed in the position of the exit pupil EP asdescribed in the principle of varying the above described projectingdirection.

In the present Embodiment 2, the first lens unit G1 is caused to have apositive refractive power in order to secure the back focus and derive abright optical system while keeping the entire zoom optical systemcompact.

Hereinafter, as the numerical embodiment 2 corresponding with Embodiment2 shown in FIGS. 3A and 3B, the configuring data of the zoom opticalsystem is shown in Table 2.

The synthesized refractive power of respective lens units that moveintegrally during zooming is positive for the first lens unit G1,negative for the second lens unit G2 (negative for the 2a-th lens subunit G2 a and positive for the 2b-th lens sub unit G2 b) and positivefor the third lens unit. That is, as described above, the configurationof the present embodiment (numerical embodiment) can be deemed as a4-lens unit configuration as shown in FIG. 13, and in this case, can betreated as the one configured by positive-negative-positive-positivelens units in order from the reduction side.

Here, in the present embodiment, respective aberrations are correctedwell by configuring the 12th surface having the largest diameter amongthe zoom optical systems as an aspherical surface. TABLE 2 <<NumericalEmbodiment 2>> Liquid crystal panel size: 0.7 inch (maximum objectheight of 8.89 mm) Focal length fz: 74.7 to 142.0 Zoom ratio: 1.90Aperture stop diameter: 40.0 surface number curvature surface objectradius interval refractive Abbe surface infinite variable index constant1 42.8622 4.4467 1.676808 40.9032 2 −708.8428 0.5862 3 35.4807 3.18651.709598 29.6932 4 25.1107 variable 5 −20.0291 6.3603 1.75163 31.3834 61734.7302 2.4873 7 −432.9913 8.7024 1.565048 63.5961 8 −35.7122 0.1 9−78.9883 8.6282 1.48749 70.4058 10 −32.4309 variable 11 179.6767 5.61951.602739 61.267 12 −151.5641 variable (aspherical surface) 13 infinite240 14 −240 0 (image plane) Aspherical surface quantity 12th surface K(conic coefficient): 10.392636 A (4th): 0.55239E−6 B (6th): 0.194218E−10C (8th): 0.215610E−12 D (10th): −0.175710.E−15 Variable interval fz 74.791.5252 108.35 125.175 142 d0 52.4229 48.4852 45.9646 45 45.8383 d48.9516 31.7698 44.2687 51 54.6467 d10 0.9779 0.1 7.283 17.9537 29.398d12 77.5306 59.5279 42.3667 25.9293 10

FIG. 11 shows, likewise the 4-lens unit configuration (the configurationof Embodiment 1), that the interval between the exit pupil and the imageside principal point position of the present numerical embodiment 2 issubstantially equal to the focal length of the zoom optical system. Asapparent from this drawing, each lens unit is arranged so that thedistance fz from the image side principal point to the exit pupilsubstantially corresponds to each focal length, and therefore, inaddition to the object surface and the image plane, the exit pupilsurface can be made immobile during zooming. That is, in the presentnumerical embodiment, likewise the zoom optical system of Embodiment 1in 4-lens unit configuration, the distance from the image side principalpoint to the exit pupil is equal to the focal length of the zoom opticalsystem.

Moreover, in FIG. 12, theoretical values of Expression (1) is indicatedwith a solid line and the actual principal point interval with eachfocal length derived by dividing the range of the focal length equallyby five is plotted with void marks. From this drawing, it is apparentthat the interval between the object side principal point and the imageside principal point of the zoom optical-system in the present numericalembodiment 2 is, likewise the zoom optical system of Embodiment 1 in4-lens unit configuration, substantially equal to the values ofExpression (1).

In addition, longitudinal aberration graphs of the present NumericalEmbodiment 2 are shown in FIG. 8. FIG. 8 shows longitudinal aberrationgraphs in-wide angle (74.7 mm focal length), middle (108.35 mm) and tele(142 mm focal length) in an order from the top. The wavelengths ofassessment light beams are 620 nm, 550 nm and 470 nm. From this drawing,it is apparent that image forming has been implemented well.

As having been described above, each zoom optical system of the abovedescribed respective embodiments secures a sufficient space forinserting color synthesizing elements etc., is excellent intelecentricity on the object side and is excellent in the immobility ofthe positions of the object surface, the image plane and the exit pupilto variation of the focal length.

Accordingly, if arranging this zoom optical system on the object surfaceside of the projecting optical system described in Embodiment 1, aprojecting optical system as well as an image projecting apparatus thatis low in sensibility to manufacturing errors and has wide view angle,nevertheless can correct aberrations well and derives a large imagemovement quantity can be realized.

Here, in the above described Embodiments 1 and 2, a zoom optical systemwith the exit pupil diameter in the Y-axis direction being differentfrom that in the X-axis direction was described, but the presentinvention is applicable also to a zoom optical system with the exitpupil having the same diameter in the both directions.

Here, the present invention is applicable also to a magnification lengthmeasuring machine.

In addition, in the above described embodiment, a zoom optical systemwith the object side being the reduction side and the image side beingthe magnification side was described, but the present invention isapplicable also to a zoom optical system with the object side being themagnification side and the image side being the reduction side as wellas an optical apparatus using this. For example, application to anexposure apparatus (if the optical system is telecentric on thereduction side, the size of an image does not vary even if a focusedposition of reduction-side object incurs a slight displacement) and acompact image pickup lens (having a stop on the magnification side ofthe zoom optical system) is feasible.

Moreover, providing a diffraction grating on the lens surface, opticalpower may be arranged to be derived and the chromatic aberration may becorrected.

According to the present embodiment, a zoom optical system that securesa sufficient back focus, is a bright optical system with a largenumerical aperture, moreover is excellent in telecentricity on theobject side and excellent in invariance of positions of the objectsurface, the image plane and the exit pupil to a variation of the focallength and, in addition, is compact can be realized.

This application claims priority from Japanese Patent Application No.2004-261717 filed on Sep. 8, 2004, which is hereby incorporated byreference herein.

1. A zoom optical system, comprising in order from a reduction side to amagnification side: a first lens unit having a positive optical power; asecond lens unit having a negative optical power; a third lens unithaving a positive optical power; and a fourth lens unit having apositive optical power, wherein respective intervals between the first,second, third and fourth lens units vary during zooming, wherein amagnification-side conjugate position with respect to a reduction-sideconjugate position and a position of a pupil of the zoom optical systemwith respect to the reduction-side conjugate position are substantiallyimmobile respectively across an entire zooming range, and wherein thefourth lens unit moves toward the magnification side and an intervalbetween the first lens unit and the fourth lens unit increases duringzooming from a wide-angle end to a telephoto end.
 2. The zoom opticalsystem according to claim 1, wherein said pupil is located outside thezoom optical system.
 3. The zoom optical system according to claim 2,wherein said pupil is located in said magnification conjugate side ofsaid lens unit.
 4. The zoom optical system according to claim 1, whereina position of said first lens unit at a telephoto end is closer to saidreduction side than a position of said first lens unit at a wide angleend is.
 5. The zoom optical system according to claim 1, wherein aposition of a lens unit on the most magnification side among saidmagnification lens units at a telephoto end is closer to a magnificationside than a position of a lens unit on the most magnification side at awide angle end is.
 6. The zoom optical system according to claim 1,wherein an interval between said first lens unit and said second lensunit at a telephoto end is wider than an interval between said firstlens unit and said second lens unit at a wide angle end, an intervalbetween said second lens unit and said third lens unit at a telephotoend is narrower than an interval between said second lens unit and saidthird lens unit at a wide angle end and an interval between said thirdlens unit and said fourth lens unit at a telephoto end is wider than aninterval between said third lens unit and said fourth lens unit at awide angle end.
 7. The zoom optical system according to claim 1, whereinthe zoom optical system is substantially telecentric on said reductionconjugate side, and wherein across said entire zooming range, a distancefrom an image side principal point to said pupil is substantially equalto a focal length of the zoom optical system.
 8. The zoom optical systemaccording to claim 1, wherein across said entire zooming range, adistance from said reduction conjugate side principal point to saidmagnification conjugate side principal point is substantially equal to:E−fz−fz(x′+fz)/x′, where E represents a distance from said reductionside conjugate position to said magnification side conjugate position,fz represents a focal length of the zoom optical system and x′represents a distance from said pupil to said magnification sideconjugate position.
 9. The zoom optical system according to claim 1,wherein across said entire zooming range, a distance from said fourthlens unit to said pupil is longer than half a minimum diameter of thepupil.
 10. A projecting optical system, comprising: a zoom opticalsystem according to claim 1, wherein a light beam from an originalarranged in said reduction conjugate position is projected onto asurface to be projected.
 11. A projecting optical system, comprising: azoom optical system according to claim 1; a reflecting member,substantially arranged in said pupil position, for reflecting light beamfrom the zoom optical system; and a reflecting optical system includinga plurality of reflecting surfaces for sequentially reflecting lightbeam from said reflecting member, wherein a light beam, which is from anoriginal arranged in said reduction conjugate position and is incidentto said zoom optical system, is projected onto a surface to be projectedby said reflecting optical system, and wherein said reflecting memberrotates so that a projected image projected onto said surface to beprojected moves on said surface to be projected.
 12. The projectingoptical system according to claim 11, wherein said reflecting opticalsystem includes a plurality of non-rotational symmetrical reflectingsurfaces.
 13. The projecting optical system according to claim 11,wherein an intermediate image of said original is formed in saidreflecting optical system.
 14. The projecting optical system accordingto claim 11, further comprising: at least one refractive optical elementarranged between said reflecting optical system and said surface to beprojected.
 15. The projecting optical system according to claim 14,wherein said at least one refractive optical element includes a cementedlens of a positive lens and a negative lens.
 16. An image projectingapparatus, comprising: a projecting optical system according to claim 11and an image forming element of forming said original.
 17. The imageprojecting apparatus according to claim 16, wherein across said entirezooming range, a distance from said reduction side conjugate position tosaid first lens unit is three times or more longer than a maximum heightof said original.
 18. An image projecting system, comprising: the imageprojecting apparatus according to claim 16 and an image informationproviding apparatus for supplying said image projection apparatus withimage information for forming said original.
 19. An optical apparatushaving the zoom optical system according to claim
 1. 20. A zoom opticalsystem, comprising in order from a reduction side to a magnificationside: a first lens unit having a positive optical power; a second lensunit having a negative optical power; and a third lens unit having apositive optical power, wherein respective intervals between said first,second and third lens units vary during zooming, a magnification-sideconjugate position with respect to a reduction-side conjugate positionand a position of a pupil of said zoom optical system with respect to areduction-side conjugate position are substantially immobilerespectively across a entire zooming range, said third lens unitapproaches a pupil and an interval between said first lens unit and saidthird lens unit increases during zooming from a wide-angle end to atelephoto end, and said second lens unit is configured, in order fromsaid reduction side to a magnification side, by a 2a-th lens sub unithaving a negative optical power and a 2b-th lens sub unit having apositive optical power.
 21. The optical system according to claim 20,wherein an interval between said first lens unit and said second lensunit at a telephoto end is wider than an interval between said firstlens unit and said second lens unit at a wide angle end and an intervalbetween said second lens unit and said third lens unit at a telephotoend is wider than an interval between said second lens unit and saidthird lens unit at a wide angle end.
 22. A projecting optical system,comprising: a zoom optical system according to claim 20, wherein a lightbeam from an original arranged in said reduction conjugate position isprojected onto a surface to be projected.
 23. A projecting opticalsystem, comprising: a zoom optical system according to claim 20; areflecting member, substantially arranged in said pupil position, forreflecting light from the zoom optical system; and a reflecting opticalsystem including a plurality of reflecting surfaces for sequentiallyreflecting light from said reflecting member, wherein a light beam,which is from an original arranged in said reduction conjugate positionand is incident to said zoom optical system, is projected onto a surfaceto be projected by said reflecting optical system, and wherein saidreflecting member rotates so that a projected image projected onto saidsurface to be projected moves on said surface to be projected.
 24. Theprojecting optical system according to claim 23, wherein said reflectingoptical system includes a plurality of non-rotational symmetricalreflecting planes.
 25. The projecting optical system according to claim23, wherein an intermediate image of said original is formed in saidreflecting optical system.
 26. The projecting optical system accordingto claim 23, further comprising: at least one refractive optical elementarranged between said reflecting optical system and said surface to beprojected.
 27. The projecting optical system according to claim 26,wherein said at least one refractive optical element includes a cementedlens of a positive lens and a negative lens.
 28. An image projectingapparatus, comprising: a projecting optical system according to claim 23and an image forming element of forming said original.
 29. The imageprojecting apparatus according to claim 28, wherein a distance from saidreduction side conjugate position to said first lens unit is three timeslonger than a maximum height of said original across said entire zoomingrange.
 30. An image projecting system, comprising: the image projectingapparatus according to claim 28 and an image information providingapparatus for supplying said image projecting apparatus with imageinformation for forming said original.
 31. An optical apparatus havingthe zoom optical system according to claim 20.